1. Field of the Invention
The present invention is directed toward computer memory, and more particularly to phase change memory utilizing phase change materials.
2. Description of Background
There are two major groups in computer memory: non-volatile memory and volatile memory. Constant (or nearly constant) input of energy in order to retain information is not necessary in non-volatile memory but is required in the volatile memory. Thus, non-volatile memory devices contain memory in which the state of the memory elements can be retained for days to decades without power consumption. Examples of non-volatile memory devices are Read Only Memory (ROM), Flash Electrical Erasable Read Only Memory, Ferroelectric Random Access Memory, Magnetic Random Access Memory (MRAM), and Phase Change Memory (PCM). Examples of volatile memory devices include Dynamic Random Access Memory (DRAM) and Static Random Access Memory (SRAM).
The present invention is directed to phase change memory. In phase change memory, information is stored in materials that can be manipulated into different phases. Each of these phases exhibit different electrical properties which can be used for storing information. The amorphous and crystalline phases are typically two phases used for bit storage (1's and 0's) since they have detectable differences in electrical resistance. Specifically, the amorphous phase has a higher resistance than the crystalline phase.
Chalcogenides are a group of materials commonly utilized as phase change material. This group of materials contain a chalcogen (Periodic Table Group 16/VIA) and another element. Selenium (Se) and tellurium (Te) are the two most common semiconductors in the group used to produce a chalcogenide when creating a phase change memory cell. Examples of this would be Ge2Sb2Te5 (GST), Sb2Te3, and In2Se3. However, problems arise in multi-element phase change materials with repeated read-write phase change cycles. The phase change materials may phase segregate, undergo local variations in stoichiometry, and in the case of doped phase change materials the dopant atoms may redistribute themselves. Thus it is desirable to devise a solution to prevent problems associated with repeated phase change cycles in phase change memory devices.